SAGINAW, Mich. (AP) - Dow DuPont is preparing to clean up the last section of a mid-Michigan river contaminated with dioxin from past operation of a Dow Chemical Co. plant in Midland. Area residents have until Nov. 20 to submit comments on the plan to the U.S. Environmental Protection Agency. Dioxin pollution extends across the lower 24 miles of the Tittabawassee River, 22 miles of the Saginaw River and portions of Lake Huron's Saginaw Bay. The latest phase of the cleanup will cover about 7 miles of the Tittabawassee. It's scheduled to begin next year. Mlive .com reports the plan includes options for dealing with dioxin buried in the river sediments and banks. Dioxin includes a group of related toxic chemicals that can cause cancer, reproductive and developmental problems, and damage to the immune system.